In a semiconductor integrated circuit, contact holes are formed in an insulating layer on an impurity diffusion layer (for example, the source or drain of a metal oxide semiconductor MOS transistor) in a substrate to electrically connect the insulating layer and metal wiring conductors. Through holes are formed in interlayer insulating films to electrically connect multi-wiring conductors.
A conventional method for making such contact structure will be described with respect to FIG. 1. First, SiO.sub.2 film 103 is formed on a Si substrate 101 on which an impurity diffusion layer 102 is formed with a source or drain of a transistor, for example. The SiO.sub.2 film 103 is then coated with a photoresist film 104 of a positive type, for example, and exposed and developed, then the photoresist film 104 is patterned so as to have openings 105 directly above the impurity diffusion layer 102.
In order to form taper portions 106 which improves step coverage of a metal wiring layer at the contact holes 107, wet isotropic etching is performed with buffered hydrogen fluoride solution BHF. Dry anisotropic etching is then performed with, for example, fluorocarbon gas being masked by the photoresist film 104 to form contact holes 107 in the SiO.sub.2 film 103.
While the above description relates to making the contact hole structure, a through hole structure is similarly constructed.
However, when the SiO.sub.2 film 103 is subjected to wet-etching with the photoresist film 104 used as the mask, adhesion of the photoresist film 104 which is generally made of an organic substance to the SiO.sub.2 film 103 is insufficient. Thus, the etching solution soaks into the interface 108 between those films 104 and 103 and hence the SiO.sub.2 film is excessively etched along the interface 108, undesirably. Thus, if the SiO.sub.2 film 103 is sufficiently etched, conductive paths would be formed between the contact concerned and adjacent contacts, disadvantageously.
JP-A-2-260553 (Morozumi) discloses a method of forming a through hole, comprising the steps of epitaxially growing a first silicon oxide film on an interlayer insulating film, reacting tetraethyl orthosilicate TEOS and ozone O.sub.3 in vapor phase upon the first silicon oxide film to deposite a second silicon oxide film superposed on the first silicon oxide film, forming a coated glass film on the second silicon oxide film, and then plasma etching those films to form the through hole. However, Morozumi neither teaches nor suggests the above problem raised by the soaking of the etching solution into the interface in the wet etching.
JP-A-5-218331 (Yokoyama) discloses a method of forming contact holes, comprising the steps of sequentially forming a TEOS oxide film, a nitride film, and an ozone TEOS film on the whole surface of a silicon substrate, flattening the ozone TEOS film, forming a resist pattern on the flattened ozone TEOS film, etching away the ozone TEOS film, nitride film and oxide film sequentially with the resist pattern used as a mask to form the contact holes in a self-adjusting manner. First, wet etching is performed on the ozone TEOS film and then dry etching is performed on the remaining films. Yokoyama proposes damaging the ozone TEOS film at the position of the contact hole to increase the wet etching rate in order to prevent lateral erosion in the wet etching. Yokoyama neither teaches nor suggests the above problem raised by the soaking of the etching solution into the interface between the ozone TEOS film and the resist pattern in the wet etching.